Exhaust heat recovery system

ABSTRACT

An exhaust heat recovery system  25  provided with a plurality of heat pipes  60, 61  provided with heat recovery parts  60   a,    61   a  and heat exchange parts  60   b,    61   b . The heat pipes recover heat from exhaust gas exhausted from an internal combustion engine at the heat recovery parts and transfer this recovered heat to an object to be heated at the heat exchange parts. The heat recovery part  60   a  of the first heat pipe  60  recovers heat from the exhaust gas at an exhaust purification catalyst  20 ′ provided in an engine exhaust passage or its upstream side. The heat recovery part  61   b  of the second heat pipe  61  recovers heat from the exhaust gas at the downstream side of the exhaust purification catalyst. Due to this, there is provided an exhaust heat recovery system which can recover at least a fixed amount of exhaust heat at all times while maintaining a warm-up performance of the exhaust purification catalyst.

TECHNICAL FIELD

The present invention relates to an exhaust heat recovery system.

BACKGROUND ART

The exhaust gas exhausted from an internal combustion engine in general is higher in temperature than the atmospheric temperature and therefore contains large heat energy. Therefore, an exhaust heat recovery system has been proposed which recovers the heat energy included in the exhaust gas and utilizes the recovered heat energy to raise the temperature of other systems of the internal combustion engine or converts the heat energy to electrical energy for storage in a battery.

As such an exhaust heat recovery system, for example, it is known to attach a heat pipe to a component part of the exhaust system of an internal combustion engine and attach a thermoelectric conversion element to this heat pipe (for example, Japanese Patent Publication (A) No. 2005-264916). By using such a heat pipe, the heat of the exhaust system can be transferred to the thermoelectric conversion element for generation of power.

In particular, in the exhaust heat recovery system described in Japanese Patent Publication (A) No. 2005-264916, to solve the problem that attaching a heat pipe to a component part of the exhaust system of an internal combustion engine ends up reducing the amount of heat contained in the exhaust gas flowing into an exhaust purification catalyst, the work start temperature of the heat pipe is set to a temperature higher than the activation temperature of the exhaust purification catalyst.

However, if setting the work start temperature of the heat pipe to a temperature higher than the activation temperature of the exhaust purification catalyst like in the exhaust heat recovery system described in Japanese Patent Publication (A) No. 2005-264916, when the temperature of the exhaust gas flowing into the exhaust purification catalyst is lower than the catalyst activation temperature, heat energy is not recovered by the heat pipe. Therefore, during this time, it is not possible to raise the temperature of other systems of the internal combustion engine requiring a rise of temperature.

Here, as a system for which a rise in temperature is required, for example, there is known a fuel separation system separating fuel supplied as a stock material (that is “stock fuel”) to produce fuels different in properties from the stock fuel. In this fuel separation system, to efficiently separate the stock fuel, it is necessary to raise the temperature of the stock fuel to a certain temperature or more. The above-mentioned exhaust heat recovery system may be used for raising the temperature of this stock fuel.

However, if using an exhaust heat recovery system such as described in the above-mentioned Japanese Patent Publication (A) No. 2005-264916, sometimes the temperature of the stock fuel flowing into the fuel separation system rises to the certain temperature or more and therefore the stock fuel cannot be efficiently separated. If it is not possible to efficiently separate the stock fuel in this way, it is not possible to maintain the optimum combustion of the internal combustion engine.

DISCLOSURE OF INVENTION

Therefore, an object of the present invention is to provide an exhaust heat recovery system able to recover at least a certain amount of exhaust heat at all times while maintaining the warm-up performance of an exhaust purification catalyst.

To achieve this object, in one aspect of the present invention, there is provided an exhaust heat recovery system provided with a plurality of heat transport devices each provided with a heat recovery part and a heat exchange part, each heat transport device recovering heat at the heat recovery part from exhaust gas exhausted from an internal combustion engine and transferring this recovered heat to an object to be heated at the heat exchange part, wherein the heat recovery part of a first heat transport device recovers heat from an exhaust purification catalyst provided in an engine exhaust passage or an upstream side of the same, while the heat recovery part of a second heat transport device recovers heat from the exhaust gas at a downstream side of the exhaust purification catalyst.

According to the above aspect, since the heat recovery part of the first heat transport device recovers heat from the exhaust gas at the exhaust purification catalyst or its upstream side, even at the time of the cold start of the internal combustion engine, it is possible to recover heat from the exhaust gas. On the other hand, since the heat recovery part of the second heat transport device recovers heat from the exhaust gas at the downstream side of the exhaust purification catalyst, it is possible to recover a large amount of heat from the exhaust gas after warm-up of the internal combustion engine.

In another aspect of the present invention, the heat transport capacities of the plurality of heat transport devices differ for each heat transport device.

In still another aspect of the present invention, a heat capacity of the first heat transport device is smaller than a heat capacity of the second heat transport device.

In still another aspect of the present invention, the heat transport devices are heat pipes, and the amount of the heat medium in the heat pipe differs between the first heat transport device and second heat transport device.

In still another aspect of the present invention, the heat exchange parts heat the fluid to be heated.

In still another aspect of the present invention, the flow rate of the fluid to be heated flowing in the heat exchange parts is controlled in accordance with the temperature of the exhaust gas exhausted from the internal combustion engine.

In still another aspect of the present invention, the heat transport devices are heat pipes and, when the temperature of the second heat transport device is lower than a reference temperature, the flow rate of the fluid to be heated flowing through the heat exchange part of the second heat transport device is made zero.

In still another aspect of the present invention, the system is further provided with a route for the fluid to be heated passing through the heat exchange part of the first heat transport device and the heat exchange part of the second heat transport device and a flow regulator valve provided in a channel between the heat exchange part of the first heat transport device and the heat exchange part of the second heat transport device, and the flow regulator valve regulates the flow rate of the fluid to be heated passing through the heat exchange part of the second heat transport device in the fluid to be heated passing through the heat exchange part of the first heat transport device.

According to the present invention, since the second heat transport device recovers the heat of the exhaust gas at the downstream side of the exhaust purification catalyst, it is possible to maintain the warm-up performance of the exhaust purification catalyst. Further, since the first heat transport device recovers the heat of the exhaust gas at the exhaust purification catalyst or its upstream side, even at the time of the cold start of the internal combustion engine, it is possible to recover a certain extent of heat. Therefore, according to the present invention, by suitably setting the heat transport capacities of the first heat transport device and second heat transport device, it is possible to recover at least a certain amount of exhaust heat while maintaining the warm-up performance of the exhaust purification catalyst.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be more clearly understood from the description as set forth below with reference to the accompanying drawings, in which:

FIG. 1 is a view showing a side cross-sectional view of a spark ignition type internal combustion engine.

FIG. 2 is a view schematically showing the schematic configuration of a fuel feed mechanism.

FIG. 3 is a schematic view of an exhaust heat recovery system of a first embodiment.

FIG. 4 is a schematic cross-sectional view along a line A-A of FIG. 3.

FIG. 5 is a graph of the relationship between the heat recovery amount of a heat recovery part of a heat pipe and the heat transfer amount able to be transferred to the heat exchange part.

FIG. 6 is a schematic view of an exhaust heat recovery system of a second embodiment.

FIG. 7 is a schematic view of an exhaust heat recovery system of a third embodiment.

FIG. 8 is a schematic view of an exhaust heat recovery system of a fourth embodiment.

BEST MODE FOR CARRYING OUT THE INVENTION

Below, referring to the drawings, an exhaust heat recovery system of a first embodiment of the present invention will be explained in detail. FIG. 1 is a side cross-sectional view of a spark ignition type internal combustion engine at which an exhaust heat recovery system is mounted.

Referring to FIG. 1, 1 indicates an engine body, 2 a cylinder block, 3 a cylinder head, 4 a piston, 5 a combustion chamber, 6 a spark plug arranged at the center of the top of the combustion chamber 5, 7 an intake valve, 8 an intake port, 9 an exhaust valve, and 10 an exhaust port. On the peripheral region of each cylinder inner wall of the cylinder head 4, a fuel injector 11 a for injecting fuel directly into the combustion chamber 5 (below referred to as “in-cylinder fuel injector”) is arranged. Each intake port 8 is connected through an intake branch pipe 12 to a surge tank 13. At each intake branch pipe 12, a fuel injector 11 b for injecting fuel toward the inside of the corresponding intake port 8 (below referred to as a “port injection fuel injector”) is arranged.

The surge tank 13 is connected through a suction duct 14 to an air cleaner 15. Inside the suction duct 14, a throttle valve 17 driven by an actuator 16 and an intake air detector 18 using for example hot wire are arranged. On the other hand, each exhaust port 10 is connected through an exhaust manifold 19 to a catalytic converter 20 housing an exhaust purification catalyst (for example three-way catalyst). The catalytic converter 20 is connected to an exhaust pipe 21. Note that below, the exhaust manifold 19, catalytic converter 20, and exhaust pipe 21 defining the exhaust passage at the downstream side of the exhaust ports 10 will be referred to all together as the “exhaust pipe 22”.

The fuel injectors 11 a, 11 b are connected to a fuel tank 23. Between the fuel injectors 11 a, 11 b and the fuel tank 23, a fuel separation system 24 is provided. The fuel separation system 24 separates the stock fuel (gasoline stored in the fuel tank 3) into high octane value fuel with a higher octane value than the stock fuel and low octane value fuel with an octane value lower than the stock fuel. Further, the exhaust pipe 22 is provided with an exhaust heat recovery system 25 recovering heat from the exhaust gas flowing through the exhaust pipe 22 and transferring heat to the heated object.

The electronic control unit 30 is comprised of a digital computer provided with a ROM (read only memory) 32, RAM (random access memory) 33, CPU (microprocessor) 34, input port 35, and output port 36 connected with each other by a bi-directional bus 31. The output signal of the intake air detector 18 is input through a corresponding AD converter 37 to the input port 35. Further, an accelerator pedal 40 is connected to a load sensor 41 generating an output voltage proportional to the amount of depression of the accelerator pedal 40. The output voltage of the load sensor 41 is input through a corresponding AD converter 37 to the input port 35. Furthermore, the input port 35 is connected to a crank angle sensor 42 generating an output pulse each time the crankshaft rotates by for example 30°. On the other hand, the output port 36 is connected through a corresponding drive circuit 38 to the spark plug 6, fuel injectors 11 a, 11 b, throttle valve drive actuator 16, and fuel separation system 24.

Next, the configuration of the vehicle-mounted fuel separation system 24 of the present embodiment will be explained with reference to FIG. 2. FIG. 2 is a view schematically showing the schematic configuration of a fuel feed mechanism.

The fuel feed mechanism shown in FIG. 2 is provided with a stock fuel tank 23, fuel separation system 24, high octane value fuel tank 51, and low octane value fuel tank 52. The stock fuel tank 23 is supplied with and stores ordinary (commercially available) gasoline. The fuel stored in the stock fuel tank 23 is separated by the fuel separation system 24 into high octane value fuel with an octane value higher than the stock fuel and low octane value fuel with an octane value lower than the stock fuel. The separated fuels are stored respectively in the high octane value fuel tank 51 and low octane value fuel tank 52.

The high octane value fuel in the high octane value fuel tank 51 is supplied by a feed pump 53 to each port injection fuel injector 11 b and injected into the intake port 8 of each cylinder. On the other hand, the low octane value fuel in the low octane value fuel tank 52 is fed by the feed pump 54 to each in-cylinder fuel injector 11 a where it is directly injected into the combustion chamber 5 of each cylinder.

In this way, in the present embodiment, mutually independent fuel injectors 11 a, 11 b are used for the low octane value fuel and for the high octane value fuel, so it is possible to selectively supply one of the low octane value fuel and high octane value fuel or simultaneously supply both of them by a predetermined ratio in accordance with the engine operating state to the combustion chamber 5 of each cylinder of the engine body 1 operating by a predetermined ratio.

Next, referring to FIG. 2, the fuel separation system 24 of the present embodiment will be explained. The fuel separation system 24 is provided with a flow control valve 55, a heat exchanger 56, a separation unit 57 having a separation membrane, a condenser/cooler gas-liquid separator 58, etc.

The separation unit 57 is configured separating a housing 57 a comprised of a heat resistant vessel into two sections 57 c, 57 d by an aromatic separation membrane 57 b. As the aromatic separation membrane 57 b, one having the property of selectively passing the aromatic components in gasoline is used. That is, in the aromatic separation membrane 57 b, if supplying stock fuel to one side (for example, the section 57 c side, that is, the low octane value fuel side) at a relatively high pressure and holding the other side (for example, the section 57 d side, that is, the high octane value fuel side) at a relatively low pressure, the aromatic components in the stock fuel mainly permeate through the separation membrane 57 b to the surface of the low pressure side (the section 57 d side, that is, the high octane value fuel side) of the separation membrane 57 b and cover the surface of the separation membrane 57 b facing the low pressure side.

By removing the permeated fuel covering the surface of this low pressure side separation membrane 57 b, the aromatic components permeate from the high pressure section 57 c side to the low pressure section 57 d side continuously through the separation membrane 57 b. In the present embodiment, by maintaining the pressure at the low pressure side (section 57 d side) at a pressure lower than the vapor pressure of the permeated aromatic component, the permeated fuel containing a large amount of aromatic components covering the low pressure side separation membrane 57 b surface is evaporated to continuously remove it from the surface and is recovered in the form of fuel vapor.

The fuel vapor recovered from the low pressure side section 57 d of the separation membrane unit 57 is sent to the condenser/cooler gas-liquid separator 58 where it is cooled. Due to this, the relatively high boiling point aromatic component liquefies. At the gas-liquid separator 58, a liquid high octane value fuel containing a large amount of aromatic components is produced. The thus produced high octane value fuel is supplied to the high octane value fuel tank 51.

On the other hand, the fuel remaining in the high pressure side section 57 c of the separation membrane unit 57 is stripped of part of its aromatic components to become smaller in high octane value component content. Therefore, in the high temperature side section 57 c of the separation membrane unit 57, a low octane value fuel with a small content of the aromatic components is produced. The thus produced low octane value fuel is fed to the low octane value fuel tank 52.

Here, the separation efficiency of the separation membrane 57 b changes according to the working conditions of this separation membrane 57 b. Therefore, to make the separation efficiency of the separation membrane 57 b high, it is necessary to suitably control the working conditions of the separation membrane 57 b. As the working conditions affecting the separation efficiency of the separation membrane 57 b, the temperature of the stock fuel supplied to the separation membrane 57 b can be mentioned.

The ratio of the amount of the aromatic components in the stock fuel passing through the separation membrane 57 b (selectivity) increases in accordance with the rise in temperature of the stock fuel from atmospheric temperature until reaching a certain temperature. This certain temperature is the temperature where the temperature of the low pressure side (section 57 d) of the separation membrane 57 b reaches a certain lower limit temperature. This lower limit temperature is a function of the low pressure side pressure of the separation membrane 57 b and for example becomes 353K (80° C.) or so at a low pressure side pressure of 5 kPa.

On the other hand, if the temperature at the low pressure side continues to rise exceeding the lower limit temperature, the selectivity falls at a certain temperature or more. That is, there is an optimum temperature range for maintaining the temperature at the low pressure side. This optimum temperature range is for example 348K to 438K (about 75° C. to 165° C.) or so at a low pressure side pressure in the range of 5 to 50 kPa.

Therefore, to maximize the separation efficiency by the separation membrane 57 b, it is necessary to maintain the temperature of the stock fuel so that the low pressure side temperature of the separation membrane 57 b becomes the optimum temperature range. For this reason, in the present embodiment, before supplying the stock fuel to the separation membrane unit 57, the heat exchanger 56 is used to heat the stock fuel to maintain the temperature whereby the separation efficiency by the separation membrane 57 b increases the most. Note that in an embodiment of the present invention, as the heat exchanger 56, the later mentioned heat exchange parts of the exhaust heat recovery system 25 are utilized.

Further, in the present embodiment, a flow control valve 55 is provided between the fuel pump 59 of the stock fuel tank 23 and the heat exchanger 56. By controlling the opening degree of this flow control valve 55, the flow rate of the supply of stock fuel to the heat exchanger 56 and separation unit 57 is controlled.

Note that the above-mentioned configuration of the fuel feed mechanism and configuration of the fuel separation system 24 are examples. As long as the fuel separation system using the heat exchanger is provided, it is possible to use any configuration of fuel feed mechanism.

Next, referring to FIG. 3, the exhaust heat recovery system 25 of a first embodiment of the present invention will be explained. As shown in FIG. 3, the exhaust heat recovery system 25 has two heat pipes 60, 61. The heat pipes 60, 61 have heat recovery part 60 a, 61 a at first ends and heat exchange parts 60 b, 61 b at the other ends. In the present embodiment, the heat recovery part 60 a of one heat pipe 60 is attached to the exhaust pipe 22 at the exhaust upstream side of the exhaust purification catalyst 20′, while the heat recovery part 61 a of the other heat pipe 61 is attached to the exhaust pipe 22 at the exhaust downstream side of the exhaust purification catalyst 20′. In the following explanation, among the two heat pipes 60, 61, the one attached to the exhaust pipe 22 at the exhaust upstream side will be referred to as the “upstream side heat pipe 60”, while the one attached to the exhaust pipe 22 at the exhaust downstream side will be referred to as the “downstream side heat pipe 61”.

FIG. 4 is a schematic cross-sectional view along the line A-A of FIG. 3. As shown in FIG. 4, in the present embodiment, the heat recovery parts 60 a, 61 a of the heat pipes 60, 61 pass through the exhaust pipe 22 and are inserted into the exhaust passage inside the exhaust pipe 22. In the heat recovery parts 60 a, 61 a, pluralities of fins 62 are attached to the side surfaces of the heat pipes 60, 61. Due to this, at the heat recovery parts 60 a, 61 a of the heat pipes 60, 61, heat is transmitted from the exhaust gas flowing through the inside of the exhaust passage to the heat pipes 60, 61.

Note that so long as the heat recovery parts 60 a, 61 a of the heat pipes 60, 61 can recover heat from the exhaust gas, not only the configuration shown in the above-mentioned FIG. 4, but various other configurations can be employed. For example, it is also possible to wrap the heat pipes 60, 61 around the exhaust pipe 22 and recover the heat through the exhaust pipe 22 from the exhaust gas flowing through the inside of the exhaust passage.

On the other hand, the heat exchange parts 60 b, 61 b of the heat pipes 60, 61 are respectively attached to fuel feed pipes 63 between the stock fuel tank 23 and separation unit 57. The heat exchange parts 60 b, 61 b of the heat pipes 60, 61, like the heat recovery parts 60 a, 61 a of the heat pipes, pass through the fuel feed pipes 63 and are inserted into the fuel passages in the fuel feed pipes 63. Due to this, in the heat exchange parts 60 b, 61 b of the heat pipes 60, 61, heat is transferred from the heat pipes 60, 61 to the fuel flowing through the fuel passage. Note that regarding the heat exchange parts 60 b, 61 b of the heat pipes 60, 61 as well, similar to the heat recovery parts 60 a, 61 a, so long as heat can be transferred to the fuel it is possible to employ not only the above configuration, but various other configurations.

The heat pipes 60, 61 are formed from hollow pipes having wicks inside. A heat medium such as water/steam is sealed in the hollow pipes. In the heat pipes 60, 61, the heat recovery parts 60 a, 61 a use the heat of the exhaust gas to evaporate the heat medium in the heat pipes 60, 61. This evaporated heat medium transfers heat to the fuel at the heat exchange parts 60 b, 61 b. Due to this, the heat medium is condensed. The condensed heat medium is again made to evaporate by the heat of the exhaust gas. According to the heat pipes 60, 61, by repeating this cycle, heat is transferred from the heat recovery parts 60 a, 61 a to the heat exchange parts 60 b, 61 b.

Therefore, in this embodiment of the present invention, the upstream side heat pipe 60 recovers heat from the exhaust gas at the heat recovery part 60 a at the exhaust upstream side of the exhaust purification catalyst 20′ and supplies the heat at the heat exchange part 60 b to the fuel flowing through the inside of the fuel feed pipe 63. On the other hand, the downstream side heat pipe 61 recovers heat from the exhaust gas at the heat recovery part 61 a at the exhaust downstream side of the exhaust purification catalyst 20′ and supplies the heat at the heat exchange part 61 b to the fuel flowing through the inside of the fuel feed pipe 63.

Further, in the embodiment of the present invention, the upstream side heat pipe and the downstream side heat pipe are made different in heat transport capacity. For example, in the present embodiment, the upstream side heat pipe is made to have a smaller heat capacity than the downstream side heat pipe.

FIG. 5 is a graph showing the relationship between the potential heat recovery amount of a heat recovery part of a heat pipe and the amount of heat able to be transferred to a heat exchange part. The solid line in FIG. 5 shows the relationship at a small heat capacity heat pipe (below referred to as a “small capacity heat pipe”), while the broken line shows the relationship at a large heat capacity heat pipe (below referred to as a “large capacity heat pipe”).

As will be understood from FIG. 5, in the case of a small capacity heat pipe, if the heat recovery amount is small, the increase of the amount of heat transfer with respect to the increase of the potential heat recovery amount is large. The amount of heat transfer rapidly rises along with an increase in the amount of heat recovery. That is, with a small capacity heat pipe, even when the amount of heat recovery at the heat recovery part is small, the heat can be transferred. Therefore, with a small capacity heat pipe, it is possible to start the transfer of heat to the heat exchange part from when the temperature of the exhaust gas flowing through the inside of the exhaust pipe 22 in the heat recovery part is low.

However, in general the amount of heat which can be transferred by a heat pipe is limited. That is, while the heat recovery amount is small, the amount of heat transfer is increased along with the increase of the heat recovery amount. However, if reaching a certain fixed amount of heat transfer (maximum heat transfer amount), the amount of heat transfer ends up no longer increasing even if the amount of potential heat recovery increases more than that. This maximum heat transfer amount differs in accordance with the capacity of the heat pipe. The smaller the capacity of the heat pipe, the smaller the maximum heat transfer amount.

Therefore, a small capacity heat pipe can recover the heat of the exhaust gas at the heat recovery part and transfer that heat to the heat exchange part when the temperature of the exhaust gas flowing through the exhaust pipe 22 is low. However, a small capacity heat pipe has a small maximum heat transfer amount, therefore even if the temperature of the exhaust gas rises, cannot transfer a large amount of heat from the heat recovery part to the heat exchange part. Conversely, a large capacity heat pipe cannot efficiently transfer heat to the heat exchange part even if recovering the heat of the exhaust gas at the heat recovery part when the temperature of the exhaust gas flowing through the exhaust pipe 22 is low. However, a large capacity heat pipe has a large maximum heat transfer amount. Therefore, if the temperature of the exhaust gas becomes high, it is possible to transfer a large amount of heat from the heat recovery part to the heat exchange part.

Note that as the method for changing the heat capacity of the heat pipe for each heat pipe, for example changing the amount of the heat medium sealed in the heat pipe can be mentioned. If reducing the amount of the heat medium sealed in the heat pipe, the heat capacity of the heat pipe can be reduced, while conversely if increasing the amount of the heat medium sealed in the heat pipe, the heat capacity of the heat pipe can be increased.

Alternatively, as the method of changing the heat capacity of the heat pipe, changing the type of the heat medium may be mentioned. If using a small heat capacity liquid as a heat medium, the heat capacity of the heat pipe can be reduced. Conversely, if using a large heat capacity liquid as a heat medium, the heat capacity of the heat pipe can be increased.

Furthermore, as the method of changing the heat capacity of the heat pipe, the number of the heat pipes may be changed. If increasing the number of the heat pipes, the heat capacity of these heat pipes as a whole becomes large, while conversely if reducing the number of the heat pipes, the heat capacity of these heat pipes as a whole becomes small. Therefore, for example, it is also possible to configure the upstream side heat pipe 60 by a single heat pipe and configure the downstream side heat pipe 61 from a plurality of heat pipes.

In this way, if making the heat capacity of the upstream side heat pipe 60 smaller and increasing the heat capacity of the downstream side heat pipe 61, at the time of the cold start of the internal combustion engine etc., it is possible to supply the necessary minimum amount of heat to the object to be heated (that is, the stock fuel flowing through the fuel feed pipe 63) while quickly raising the temperature of the exhaust purification catalyst 20′. The reason why this sort of effect is obtained with this embodiment will be explained below.

At the time of the cold start of the internal combustion engine, the exhaust purification catalyst 20′ is not raised to the activation temperature. Therefore, to raise the purification performance with respect to the exhaust gas, it is necessary to raise the temperature of the exhaust purification catalyst 20′. However, if arranging a large capacity heat pipe at the exhaust upstream side of the exhaust purification catalyst 20′ to recover heat from the exhaust gas, a large amount of the heat of the exhaust gas ends up being recovered by the large capacity heat pipe, so the temperature of the exhaust gas flowing into the exhaust purification catalyst 20′ falls considerably from the temperature of the exhaust gas exhausted from the engine body 1. For this reason, the exhaust purification catalyst 20′ can no longer be quickly raised in temperature. On the other hand, if arranging a small capacity heat pipe at the exhaust upstream side of the exhaust purification catalyst 20′ to recover heat from the exhaust gas, the heat of the exhaust gas recovered by the small capacity heat pipe is small, so the temperature of the exhaust gas flowing into the exhaust purification catalyst 20′ will not change much at all from the temperature of the exhaust gas exhausted from the engine body 1. For this reason, it is possible to quickly raise the temperature of the exhaust purification catalyst 20′.

In particular, when like in the present embodiment the fluid to be heated is stock fuel and the stock fuel is heated to separate it, it is not necessary to heat a large amount of the stock fuel from the time of the cold start of the internal combustion engine. That is, at the time of the cold start of the internal combustion engine, usually idling operation is performed, so the amount of fuel to be injected from the fuel injectors is small. For this reason, the amount of fuel to be separated is also small. Therefore, at the time of the cold start of the internal combustion engine, it is not necessary to heat a large amount of stock fuel. For this reason, at the time of the cold start of the internal combustion engine, if using a small capacity heat pipe to heat the fuel, it is possible to heat the necessary minimum amount of stock fuel. In the present embodiment, a small capacity upstream side heat pipe 60 is provided at the exhaust upstream side of the exhaust purification catalyst 20′, so it is possible to heat the necessary minimum amount of stock fuel at the time of the cold start of the internal combustion engine.

However, as stated above, the small capacity heat pipe has a small maximum heat transfer amount, so if using only a small capacity heat pipe, a sufficient amount of stock fuel cannot be heated even if the exhaust purification catalyst 20′ is sufficiently raised in temperature. As opposed to this, in the present embodiment, at stated above, a large capacity downstream side heat pipe 61 is provided at the exhaust downstream side of the exhaust purification catalyst 20′. After the exhaust purification catalyst 20′ is sufficiently raised in temperature, the temperature of the exhaust gas exhausted from the exhaust purification catalyst 20′ is relatively high. Therefore, by providing a large capacity downstream side heat pipe 61 at the exhaust downstream side of the exhaust purification catalyst 20′, the exhaust purification catalyst 20′ is sufficiently raised in temperature, then this large capacity downstream side heat pipe 61 can recover a large amount of heat from the exhaust gas exhausted from the exhaust purification catalyst 20′. As a result, it is possible to sufficiently heat the fluid to be heated, that is, the stock fuel.

In this way, according to this embodiment of the present invention, at the time of the cold start of the internal combustion engine, the necessary minimum amount of heat can be recovered without causing almost any deterioration of the warm-up performance of the exhaust purification catalyst 20′ and a large amount of heat can be recovered after warm-up of the internal combustion engine. That is, at the time of the cold start of the internal combustion engine, it is possible to supply heat of at least the necessary minimum amount of heat to the object to be heated at all times while quickly raising the temperature of the exhaust purification catalyst 20′.

Further, when employing the configuration of the above-mentioned exhaust heat recovery system 25, it is also possible to arrange the heat recovery part 60 a of the upstream side heat pipe 60 and the immediate exhaust downstream side of the exhaust port 10. Due to this, even at the time of the cold start of the internal combustion engine, it is possible to reliably recover heat from the exhaust gas and heat the stock fuel.

Further, in the present embodiment, the flow rate of the stock fuel flowing through the heat exchange parts 60 a, 61 a of the heat pipes 60, 61 is controlled by the flow control valve 55 in accordance with the temperature of the exhaust gas exhausted from the engine body 1. Specifically, the lower the temperature of the exhaust gas exhausted from the engine body 1, the smaller the flow rate of the stock fuel flowing through the heat exchange parts 60 a, 61 a of the heat pipes 60, 61. As the temperature of the exhaust gas exhausted from the engine body 1 becomes higher, the flow rate of the stock fuel flowing through the heat exchange parts 60 a, 61 a of the heat pipes 60, 61 is increased.

That is, to efficiently separate the stock fuel in the separation unit 57 in the above-mentioned way, it is necessary to make the low pressure side temperature of the separation membrane 57 b within the predetermined optimum temperature range. However, if making the stock fuel flowing through the heat exchange parts 60 a, 61 a of the heat pipes 60, 61 fixed, in the case where the amount of heat recovered from the exhaust gas by the heat pipes 60, 61 is too small or the amount of heat is too great, the temperature of the stock fuel flowing into the separation unit 57 ends up becoming too low or too high. In such a case, the low pressure side temperature of the separation membrane 57 b may be kept within the optimum temperature range by controlling the stock fuel flow rate.

Here, the amount of heat recovered by the heat pipes 60, 61 from the exhaust gas depends on the temperature of the exhaust gas flowing through the heat recovery parts 60 a, 61 a of the heat pipes. The higher this temperature of the exhaust gas, the greater the amount of heat recovered and thereby the greater the amount of heat transferred to the stock fuel. Therefore, as the temperature of the exhaust gas exhausted from the engine body 1 becomes higher, it is possible to increase the flow rate of the stock fuel flowing through the heat exchange parts 60 a, 61 a of the heat pipes 60, 61 to maintain the temperature of the stock fuel within a certain temperature range.

Next, referring to FIG. 6, a second embodiment of the present invention will be explained. The configuration of the exhaust heat recovery system 25′ of the second embodiment is basically the same as the configuration of the exhaust heat recovery system 25 of the first embodiment. However, in the second embodiment, as shown in FIG. 6, the heat recovery part 60 a of the upstream side heat pipe 60 is attached not at the exhaust upstream side of the exhaust purification catalyst 20′, but at the exhaust purification catalyst 20′ itself or the catalytic converter 20 housing the exhaust purification catalyst 20′.

In this way, by attaching the heat recovery part 60 a of the upstream side heat pipe 60 to the exhaust purification catalyst 20′ itself or the catalytic converter 20 housing the exhaust purification catalyst 20′, the exhaust gas exhausted from the engine body 1 flows into the exhaust purification catalyst 20′ without the heat pipes 60, 61 absorbing heat. For this reason, in particular at the time of the cold start of the internal combustion engine, it is possible to warm up the exhaust purification catalyst 20′ faster.

Further, by integrally forming the exhaust purification catalyst 20′ and the heat recovery part 60 a of the heat pipe 60 or by integrally forming the catalytic converter 20 and the heat recovery part 60 a of the heat pipe 60, the mountability of these integrated parts in a vehicle is improved.

Next, referring to FIG. 7, a third embodiment of the present invention will be explained. The configuration of the exhaust heat recovery system 25″ of the third embodiment is basically similar to the configuration of the exhaust heat recovery systems 25, 25′ of the first embodiment or second embodiment. However, in the third embodiment, a route switching valve 64 is provided at the fuel feed pipe 63 between the heat exchange part 60 b of the upstream side heat pipe 60 and the heat exchange part 61 b of the downstream side heat pipe 61.

As shown in FIG. 7, between the heat exchange part 60 b of the upstream side heat pipe 60 and the heat exchange part 61 b of the downstream side heat pipe 61, a bypass pipe 65 is branched from the fuel feed pipe 63. The branching point of this bypass pipe 65 is provided with a route switching valve 64. The bypass pipe 65 bypasses the heat exchange parts 61 b of the downstream side heat pipe 61 and is directly communicated with the high pressure section 57 c of the separation unit 57. The length of this bypass pipe 65 is shorter than the length of the fuel feed pipe 63 from the branching point to the separation unit 57. The route switching valve 64 can switch between an inflow position making the stock fuel flowing out from the heat exchange part 60 b of the upstream side heat pipe 60 flow into the heat exchange part 61 b of the downstream side heat pipe 61 and a bypass position making the fuel flowing out from the heat exchange part 60 b of the upstream side heat pipe 60 flow to the bypass pipe 65.

Therefore, when the route switching valve 64 is at the inflow position, the fuel of the stock fuel tank 23 passes through the two heat exchange parts of the heat exchange part 60 b of the upstream side heat pipe 60 and the heat exchange part 61 b of the downstream side heat pipe 61. On the other hand, when the route switching valve 64 is at the bypass position, the fuel of the stock fuel tank 23 passes through only the heat exchange part 60 b of the upstream side heat pipe 60 and does not pass through the heat exchange part 61 b of the downstream side heat pipe 61.

In the present embodiment, when the temperature of the downstream side heat pipe 61 (that is, the temperature of the heat medium sealed in the downstream side heat pipe 61) is lower than a certain fixed reference temperature, the route switching valve 64 is set to the inflow position and the stock fuel flows through the two heat exchange parts 60 b, 61 b. On the other hand, when the temperature of the downstream side heat pipe 61 is the reference temperature or more, the route switching valve 64 is set to the bypass position and the stock fuel flows through only the heat exchange parts 60 b of the upstream side heat pipe 60.

Here, when the temperature of the downstream side heat pipe 61 is low, the stock fuel is not raised in temperature much at the heat exchange part 61 b of the downstream side heat pipe 61. For this reason, when the temperature of the downstream side heat pipe 61 is low, if passing through the fuel feed pipe 63 downstream of the branching point, the stock fuel loses heat by the atmosphere around the fuel feed pipe 63 while flowing through the inside of the fuel feed pipe 63 downstream of the branching point. The stock fuel ends up falling in temperature before flowing into the separation unit 57.

In the present embodiment, when the temperature of the downstream side heat pipe 61 is low, the stock fuel flows through the bypass pipe 65 into the separation unit 57. The length of the bypass pipe 65 is shorter than the length of the fuel feed pipe 63 downstream of the branching point, so while the stock fuel is flowing through the bypass pipe 65, the amount of heat lost to the atmosphere around the bypass pipe 65 is small and therefore the temperature of the stock fuel does not fall much before flowing into the separation unit 57. Therefore, according to the present embodiment, the heat of the exhaust gas can be efficiently supplied to the stock fuel flowing into the separation unit 57.

Note that the reference temperature is for example made the temperature of the downstream side heat pipe 61 whereby the temperature of the stock fuel flowing into the separation unit 57 becomes equal both when the making the stock fuel flow through the bypass pipe 65 to the separation unit 57 and when making the stock fuel flow through the fuel feed pipe 63 to the separation unit 57.

Further, in the above embodiments, the route carrying the stock fuel is changed in accordance with the temperature of the downstream side heat pipe 61, but it is also possible to change the route carrying the stock fuel in accordance with not only the temperature of the downstream side heat pipe 61, but also other parameters (for example, the time elapsed after starting the internal combustion engine etc.)

Further, it is also possible to switch the positions of the route switching valve 64 in accordance with the temperature of the downstream side heat pipe 61 and the opening degree of the flow control valve 55. That is, it is also possible to set the route switching valve 64 in the bypass position when the temperature of the downstream side heat pipe 61 is extremely high and the opening degree of the flow control valve 55 is small and to set the route switching valve 64 at the inflow position at other times.

That is, if the opening degree of the flow control valve 55 is small, the flow rate of the stock fuel flowing through the fuel feed pipe 63 is small. Further, if the temperature of the downstream side heat pipe 61 is high, the amount of heat supplied to the stock fuel in the heat exchange part 61 b of the downstream side heat pipe 61 becomes greater. In this case, if the stock fuel runs the heat exchange part 61 b of the downstream side heat pipe 61, the stock fuel ends up being excessively heated and deterioration of the fuel ends up occurring. Therefore, in such a case, by preventing the stock fuel from flowing to the heat exchange part 61 b of the downstream side heat pipe 61, overheating of the stock fuel can be prevented.

Furthermore, in the above embodiments, a route switching valve 64 is provided at the branching point of the bypass pipe 65, but instead of the route switching valve 64, it is also possible to provide a flow regulator valve able to regulate the flow rate of the fuel flowing into the fuel feed pipe 63 and bypass pipe 65 downstream of the branching point. Due to this, it is possible to adjust the flow rate of the stock fuel flowing through the inside of the fuel feed pipe downstream of the branching point in accordance with the temperature of the downstream side heat pipe 61.

Next, referring to FIG. 8, a fourth embodiment of the present invention will be explained. The configuration of the exhaust heat recovery system 25′″ of the fourth embodiment is basically similar to the configuration of the exhaust heat recovery system 25″ of the third embodiment. However, in the fourth embodiment, the route switching valve 64 and the bypass pipe 65 are not provided. Instead, two of each of the fuel feed pipe and flow control valve are provided.

That is, as shown in FIG. 8, in the fourth embodiment, two fuel feed pipes 63 a, 63 b are provided between the stock fuel tank 23 and the separation unit 57. The fuel feed pipes 63 a, 63 b are provided with flow control valves 55 a, 55 b, respectively. The heat exchange part 60 b of the upstream side heat pipe 60 is attached to the first fuel feed pipe 63 a, while the heat exchange part 61 b of the downstream side heat pipe 61 is attached to the second fuel feed pipe 63 b.

In the present embodiment, when the temperature of the downstream side heat pipe 61 is lower than a certain fixed reference temperature, only the flow control valve 55 a provided at the first fuel feed pipe 63 a is opened. The flow control valve 55 b provided at the second fuel feed pipe 63 b is not opened. On the other hand, when the temperature of the downstream side heat pipe 61 is the reference temperature or more, the two flow control valves 55 a, 55 b are opened. Due to this, in the same way as the third embodiment, it is possible to efficiently supply the heat of the exhaust gas to the stock fuel flowing into the separation unit 57.

Note that in the present embodiment as well, it is also possible to adjust the opening degree of the second flow control valve 55 b in accordance with the temperature of the downstream side heat pipe 61 and the flow rate of the stock fuel to be supplied from the stock fuel tank 23 to the separation unit 57 in the same way as the third embodiment. That is, it is also possible to close the second flow control valve 55 b when the temperature of the downstream side heat pipe 61 is extremely high and the flow rate of the stock fuel to be supplied from the stock fuel tank 23 to the separation unit 57 is small and to open the second flow control valve 55 b at other times. Due to this, overheating of the stock fuel can be prevented.

While the invention has been described by reference to specific embodiments chosen for purposes of illustration, it should be apparent that numerous modifications could be made thereto by those skilled in the art without departing from the basic concept and scope of the invention. 

1. An exhaust heat recovery system provided with a plurality of heat transport devices each provided with a heat recovery part and a heat exchange part, each heat transport device recovering heat at the heat recovery part from exhaust gas exhausted from an internal combustion engine and transferring this recovered heat to an object to be heated at the heat exchange part, wherein the heat recovery part of a first heat transport device recovers heat from an exhaust purification catalyst provided in an engine exhaust passage or an upstream side of the same, while the heat recovery part of a second heat transport device recovers heat from the exhaust gas at a downstream side of said exhaust purification catalyst.
 2. An exhaust heat recovery system as set forth in claim 1, wherein the heat transport capacities of said plurality of heat transport devices differ for each heat transport device.
 3. An exhaust heat recovery system as set forth in claim 2, wherein said first heat transport device has a heat capacity smaller than a heat capacity of the second heat transport device.
 4. An exhaust heat recovery system as set forth in claim 3, wherein said heat transport devices are heat pipes, and the amount of the heat medium in the heat pipe differs between the first heat transport device and second heat transport device.
 5. An exhaust heat recovery system as set forth in claim 1, wherein said heat exchange parts heat the fluid to be heated.
 6. An exhaust heat recovery system as set forth in claim 5, wherein the flow rate of the fluid to be heated flowing in the heat exchange parts is controlled in accordance with the temperature of the exhaust gas exhausted from said internal combustion engine.
 7. An exhaust heat recovery system as set forth in claim 5, wherein said heat transport devices are heat pipes and, when the temperature of said second heat transport device is lower than a reference temperature, the flow rate of the fluid to be heated flowing through the heat exchange part of said second heat transport device is made zero.
 8. An exhaust heat recovery system as set forth in claim 5, wherein the system is further provided with a route for the fluid to be heated passing through the heat exchange part of said first heat transport device and the heat exchange part of said second heat transport device and a flow regulator valve provided in a channel between the heat exchange part of said first heat transport device and the heat exchange part of said second heat transport device, and said flow regulator valve regulates the flow rate of the fluid to be heated passing through the heat exchange part of said second heat transport device in the fluid to be heated passing through the heat exchange part of said first heat transport device. 